As a method of making toner particles, a method employing the use of emulsion polymerization to form the toner resin binder is known. Emulsion polymerization comprises forming an emulsion of a surfactant and monomer in water, then polymerizing the monomer in the presence of a water soluble initiator. Emulsion polymerization is a well known industrial process. In forming toner compositions for use with reprographic or xerographic print devices, emulsion aggregation processes are known. For example, emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in a number of Xerox patents, such as U.S. Pat. Nos. 5,290,654, 5,278,020, 5,308,734, 5,370,963, 5,344,738, 5,403,693, 5,418,108, 5,364,729, and 5,346,797. Also of interest may be U.S. Pat. Nos. 5,348,832, 5,405,728, 5,366,841, 5,496,676, 5,527,658, 5,585,215, 5,650,255, 5,650,256, 5,501,935, 5,723,253, 5,744,520, 5,763,133, 5,766,818, 5,747,215, 5,827,633, 5,853,944, 5,804,349, 5,840,462, and 5,869,215, the disclosures of each of which are totally incorporated herein by reference.
In addition, the following U.S. patents relate to emulsion aggregation processes of forming toner compositions, the disclosures of each of which are totally incorporated herein by reference in their entireties:
U.S. Pat. No. 5,945,245 describes a surfactant free process for the preparation of toner comprising heating a mixture of an emulsion latex, a colorant, and an organic complexing agent.
U.S. Pat. No. 5,977,210 describes a process for the preparation of ink compositions comprising the emulsion polymerization of monomer, water, surfactant, and initiator with stirring and heating to provide a latex; mixing therewith a pigment dispersion of pigment particles, water, and cationic surfactant; blending the mixture; thereafter stirring the mixture; and subsequently adding additional anionic surfactant to stabilize the aggregate particles.
U.S. Pat. No. 6,458,501 describes a process for making silica-containing latex particles involves polymerizing monomer in an emulsion comprising the monomer, water, silica particles, and optionally at least one surfactant, by adding at least one free radical initiator to the emulsion to form the silica-containing latex particles.
The appropriate components and process aspects of the each of the foregoing U.S. patents may be selected for the present compositions and processes in embodiments thereof.
Generally, sulfonated polyester (SPE) resins for emulsion/aggregation (EA) toner have been made by bulk polycondensation reactions in a reaction vessel followed by discharge from the reaction vessel. When the desired molecular weight/viscosity is obtained, the viscous resin is discharged into drums and cooled. The SPE resin is then crushed and milled before being dissipated into water at elevated temperatures (for example, about 80° C. to about 150° C.) to form the latex, given that the resin has sufficient sulfonated monomer to dissipate readily. The resulting latex is mixed with pigments, wax and other additives to form toner particles. Current processes have a number of disadvantages: 1) The resin may become so viscous that discharge may be difficult, if not impossible. This is especially important for branched resins. 2) The reactor needs to be cleaned with solvent to remove any residual resin. 3) The crushing/grinding step is labor-intensive. 4) Resins with lower sulfonation levels, such as, for example, resins that are about 0.5% to about 3.75% sulfonated, cannot be readily dissipated into water without the aid of surfactants or co-solvents.
There remains a need for an improved emulsion polymerization process for preparing polyester resins. There further for an improved method for preparing emulsion aggregation toners wherein the latex is formed by emulsion polymerization.